The proposed research will integrate experimental and theoretical descriptions of the dosimetry of laser and conventional light sources for therapeutic and diagnostic applications in medicine. One goal is the development of experimental techniques to specify tissue optical properties, and measurement of a variety of tissue types to yield a LIBRARY of tissue optical properties over the ultraviolet-visible-near infrared spectrum. A second goal is COMPUTER SIMULATION OF RADIATIVE TRANSPORT in complex turbid tissues. Steady-state dosimetry will be studied in homogeneous and heterogeneous tissues for variable boundary conditions and geometries of irradiation. Time-variant dosimetry will be studied in which thermally induced changes in tissue optical properties dynamically alter dosimetry during the laser exposure. The research involves computer simulations, phantom tissue models, and in vitro and in vivo animal experiments. The research goals would aid the development of therapeutic protocols and optical devices for dosimetry and diagnostics. Three clinical situations will be considered to focus the general concepts: (1) laser therapy of portwine stain lesions, (2) screening pigmented nevi for melanoma. and (3) NdYAG irradiation of bladder and prostate during surface cooling by irrigation. The work will be conducted in a basic research laboratory within a hospital environment and motivated to yield information pertinent to practical clinical applications.